This paper studies gender differences in the allocation of workers across jobs of different complexity using panel data on Finnish metalworkers. These data provide a measure for the complexity of the workers' tasks that can be used to construct a complexity ladder of jobs. We study whether women have to meet higher productivity requirements than men in order to be assigned to more complex tasks. Gender differences in the promotion rates are examined. We use productivity measures that are based on the supervisors' performance evaluations and examine gender differences in the productivity of promoted and non-promoted workers. It is found that women start their careers in less complex tasks than men and that they are also less likely to get promoted than men who start in similar tasks. When we compare the productivity of men and women, both at the initial assignment and when some of these individuals have been promoted, we find that there is no gender-related productivity differential at the time of the initial assignment, but women become on average more productive than men afterwards, both in promoted and non-promoted subsets. The most plausible interpretation of these results is that women face a higher promotion threshold than men.